In the course of an experimental study of the fragment characteristic after neutron induced fission of 238U with incident neutron energies between 1.2 and 5.8 MeV fission-mode calculations in the frame of the multi-modal random neck-rupture model have been performed. During these calculations some technical parts of the model have been revised. The identification of fission modes is now based on unequivocal and reproducible criteria. The Ralyleigh criterion has consequently been applied to determine each possible scission configuration. The most remarkable new results are, that all physically relevant fission modes branches off in the second potential minimum exhibiting different outer barriers, and that the total kinetic energy distribution of the fission fragments is a direct consequence of the Rayleigh criterion. The fragment characteristics as the mean mass, the mean total kinetic energy and the corresponding width obtained from the fission-mode calculations compare reasonably well with the experimental findings.
For the first time the weighted fission cross-sections through each particular fission mode have been analyzed simultaneously using a Hill-Wheeler expression for the transmission through a double-humped fission barrier. The results support the picture of individual outer barriers with slightly different penetrabilities and a slightly lower inner barrier.